Neutral Loop with Inverter Bypass Circuit

[PWDickerson]

How are folks avoiding neutral loops when setting up 120/240V PV/battery inverter systems that include an inverter bypass switch. The attached schematics show how two inverter manufacturers recommend installing a bypass switch, and both diagrams are a little squirrelly about how they show the neutral wiring. One has the neutral conductor suspiciously skirting around the transfer switch, and the other leaves it up to your imagination how the neutral gets into and out of the inverter. I think most people are using ferrous metal enclosures/gutters/disconnects somewhere in their systems, so it seems to me that 215.4(B) and 300.20 require that the neutral conductor be routed with the line conductors through the inverter and also through the bypass switch directly to the inverter. This creates two neutral paths from the backup panel back to the utility transformer, which is an issue. We have been addressing this issue by specifying a 3-pole double-throw transfer switch and switching the Neutral along with L1 and L2 in the bypass switch. This is effective, but expensive. Is there a better way to do this?

 

[synchro]

Are there significant unbalanced currents going through L1 and L2 of the PV 2-pole disconnect that require a neutral conductor to be routed along with them?

 

[PWDickerson]

The inverter feeds a residential load center. There will certainly be unbalance loads, and at times may be significant.

 

[wwhitney]

What I did in a similar situation was simply collapse the loop. That is, in your second diagram, the conductors shown going directly from the manual transfer switch to the inverter would be rerouted through the enclosures of the "200A Feeder Tap Breaker" (sic) and the PV disconnect. With the duplicate neutral conductor eliminated, obviously.

Cheers, Wayne

 

[PWDickerson]

Yes, "collapsing the loop" works well when all the equipment is nicely arranged on a single wall and you can build it how you want it. Sometimes existing conditions make that hard to do, and a 3-pole switch starts to look like a better solution.